What is the area of the triangle with vertices $(1,2,3)$, $(2,5,-1)$ and $(-1,1,2) ?$

• Correct answer
  A

  $\frac{\sqrt{155}}{2}$ square units
• B

  $\frac{\sqrt{175}}{2}$ square units
• C

  $\frac{\sqrt{155}}{4}$ square units
• D

  $\frac{\sqrt{175}}{4}$ square units

Hence, the correct answer is option: 'A'.